Field of the Invention
The present invention relates to a process and an apparatus for building tyres.
In more detail, the invention is directed to the process and equipment used for building a green tyre to be subsequently submitted to a vulcanisation cycle so as to obtain the final product.
Description of the Related Art
A tyre for vehicle wheels generally comprises a carcass structure including at least one carcass ply having respectively opposite end flaps in engagement with respective annular anchoring structures, integrated into the regions usually identified as “beads”, having an inner diameter substantially corresponding to a so-called “fitting diameter” of the tyre on a respective rim.
Associated with the carcass structure is a belt structure comprising one or more belt layers, positioned in radially superposed relationship with respect to each other and to the carcass ply and having textile or metallic reinforcing cords with a crossed orientation and/or substantially parallel to the circumferential extension direction of the tyre. A tread band, also of elastomeric material like other semifinished products constituting the tyre, is applied to the belt structure, at a radially external position.
Respective sidewalls of elastomeric material are in addition applied, at an axially external position, to the side surfaces of the carcass structure, each extending from one of the side edges of the tread band until close to the respective annular anchoring structure to the beads.
In tyres of the “tubeless” type, an airtight coating layer, usually referred to as “liner” covers the inner surfaces of the tyre.
Subsequently to building of the green tyre carried out through assembling of respective components, a vulcanisation and moulding treatment is generally executed which aims at determining the structural stabilisation of the tyre through cross-linking of the elastomeric compounds and also at impressing said tyre with a desired tread pattern and possible distinctive graphic marks at the sidewalls.
The carcass structure and belt structure are generally made separately in respective work stations, to be mutually assembled at a second time.
In more detail, manufacture of the carcass structure first contemplates application of the carcass ply or plies onto a building drum so as to form a so-called “carcass sleeve” that is substantially cylindrical. The annular anchoring structures to the beads are fitted or formed on the opposite end flaps of the carcass ply or plies that are subsequently turned up around the annular structures themselves so as to enclose them loop-wise.
At the same time, a so-called “outer sleeve” is formed on a second or auxiliary drum, which outer sleeve comprises the belt layers applied in mutual radially superposed relationship, and possibly the tread band applied at a radially external position to the belt layers. The outer sleeve is then picked up from the auxiliary drum to be coupled to the carcass sleeve. To this aim, the outer sleeve is disposed in coaxial relationship around the carcass sleeve, and then the carcass sleeve or sleeves are shaped into a toroidal configuration by mutual axial approaching of the beads and simultaneous admission of fluid under pressure into the carcass sleeve, so as to determine radial expansion of the carcass plies until causing adhesion of same against the inner surface of the outer sleeve.
Concurrently with application of the carcass ply/plies against the radially internal surface of the outer sleeve, coupling of the radially external apices of the sidewalls to respective axially external end portions of the tread band is also determined. In more detail, the end portions of the tread band can be disposed in radially superposed relationship relative to the radially external apices of the sidewalls, to define a construction configuration of the so-called “underlying sidewall” type. Alternatively, the radially external apices of the sidewalls can be axially superposed on the axially external end portions of the tread band, according to a construction configuration of the so-called “overlying sidewall” type.
Assembling between the carcass sleeve and the outer sleeve can be carried out on the same drum as used for making the carcass sleeve, in which case the process is referred to as “unistage process” or “building process carried out in a single stage”.
Also known are building processes of the so-called “two-stage” type in which a so-called “first-stage drum” is used for making the carcass sleeve, while assembly between the carcass sleeve and outer sleeve is carried out on a so-called “second-stage drum” or “shaping drum”, onto which the carcass sleeve picked up from the first-stage drum and subsequently the outer sleeve picked up from the auxiliary drum are transferred.
U.S. Pat. No. 3,826,297 contemplates use of a dismountable first-stage drum to enable disengagement of the carcass sleeve, previously formed by positioning annular anchoring structures against side shoulders provided on the drum, and subsequently forming the carcass ply or plies through application of circumferentially consecutive strip-like elements, to cover the circumferential extension of the first-stage drum.
EP 1211057 proposes formation of sidewalls by winding up a continuous elongated element of raw elastomeric material into coils disposed in axially approached and/or radially superposed relationship on the carcass sleeve shaped into a toroidal conformation, so as to couple it to the outer sleeve positioned around it. Manufacture of the sidewalls can be carried out either before completing the carcass sleeve conformation, so as to obtain a construction scheme of the “underlying sidewall” type, or when conformation has been completed, so as to obtain a construction scheme of the “overlying sidewall” type.
EP 1358998 proposes manufacture of a carcass sleeve on a first-stage drum, which carcass sleeve comprises a pair of annular anchoring structures fitted around the axially opposite end flaps of a carcass ply disposed around the drum itself. The end flaps of the carcass ply are turned up around the annular anchoring structures; afterwards, manufacture of the sidewalls is carried out, through winding of at least one continuous elongated element of raw elastomeric material into coils disposed in axially approached and/or radially superposed relationship on the carcass sleeve.